Piston and method of making



July w, 1938. G, D, ELTY 2,124,360

PISTON AND METHOD OF MAKING Filed May 7, 1955 inventor 6OZ6 JO/VAZD W51 7 V LIttonwgS UNITEDSTATES OFFlCE 2,124,360 PISTON AND METHOD or MAKING George Donald Weity, Cleveland, Ohio, assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania 1 Application May '1', 1935, Serial No. 20,22

14 Claims. (o1. 29-1565) This invention relates to pistons for internal combustion engines and more particularly to improvements in pistons and methods of making pistons of aluminum or other light metal alloy having a band of relatively hard wear resistant metal arranged in the body of the piston to carry the piston rings.

Aluminum or light metal alloy pistons have been developed which possess the characteristics most desirable in a piston and in general use have replaced pistons made of the relatively heavy ferrous metals. Certain uses of light metal pistons are found,- however, which adversely afiect the life of the piston because of excessive wear of 1 the top piston rings in the grooves normally formed in the body of the piston. An instance of this is found in engines'of the Diesel type where the fuel used is more or less unrefined such as crude petroleum. At the high temperatures de- 20 veloped in this type of engine the piston is rendered less resistant to the chemical and abrasive action of undesirable 'fuel constituents found in the crude petroleum and where the piston rings are mounted directly in grooves formed in the light metal piston body excessive and rapid wear takes place. The slightest wear in the grooves permits the inertia of the parts to eiiect a vertical movement of the piston ring with respect to the piston at each reciprocation and the continued 30 reversal of vertical movement between the ring and the piston results in a battering action upon the upper and lower walls of the grooves. The battering widens the grooves and the breakage of the rings caused by playin the grooves 35 -usually results in damage to the engine.

It is extremely desirable to reduce wear of the piston ring bands and its attendant disadvantages. Prior eflorts to eliminate this trouble have included casting of an aluminum or light metal 40 alloy piston within a wear resistant band of steel or analogous material. The insert cast bands, however, having a different coefiicient of expansion than the light metal body of the piston do not shrink with the piston subsequent to casting and 45 thus separate circumferentially from the cast piston and the entire band when loosened in service produces a condition less desirable than the condition sought to be corrected.

Other efiorts to support the piston rings in 50 wear resistant bands have proposed to shrink the bands in position on a ledge or annular step out at the top of the piston. This type of construction is open to the objection that after the band has been repeatedly stressed by the expansion and 55 contraction it is unable to maintain a firm shrunk fit and not being mechanically interlocked becomes separated from the body'of the piston. Failure, of this type of piston is more serious than the failure of the insert cast type, since the separated ring is free within the cylinder and is sub- 5 jected to the reciprocating actionof the piston and may be forced through the head or side walls of the cylinder by the piston.

It is'among the objects of this invention to provide a piston and method of making the same 10 wherein the piston will have a wear resistant ring supporting band or groove adapter firmly joined to the piston body by overhanging upset portions of the piston body. A further object of the invention is to provide a piston and method of making same wherein a wearresistant ring supporting band is shrunk in position between overhanging piston body portions. A further object of the invent-ion is to provide a method of securing a wear resistant ring supporting band 'to the body of the piston by upsetting an overhanging band retaining flange subsequent to the positioning of the band'on the body of the piston. A further object of the invention is to provide a forged or upset piston with a wear resistant ring supporting hand.- Other objects relating to details of construction and economies of manufacture' will appear hereinafter.

In the accompanying drawing which illustrates preferred embodiments of the invention:

. Figure 1 is a sectional view of piston taken on a plane normal to the wrist pin axis showing the piston as arranged in the dies of a forging machine;

Figure 2 is a fragmentary sectional showing of a finished piston subsequent to the upsetting and milling operations;

Figure 3 is a plan view of a piston and wear resistant band assembled prior to the upsetting operation;

Figure 4 is a fragmentary sectional view of a modified form of piston constructed according to my invention;

Figure 5is a plan view of the modification illustrated in Figure 4.

Referring to the drawing, the pistons illustrated in Figures 1 to 5, are generally referred to as the full trunk type of piston including an integrally formed head, cylindrical ring flange depending therefrom and skirt portion having diametrically opposed pin bosses thereon. It will be understood, of course, that the invention is not limited to this or any other particular type of piston. In the preferred embodiment of my invention as illustrated in Figure 1 an annular step or ledge is milled or otherwise formed about the circumference of the upper edge of the piston to provide an upwardly extending cylindrical portion indicated by the dotted line Ilia. A wear resistant band or ring adapter H is positioned on the piston as shown and the parts arranged in a forging machine or heavy duty press and the head portion indicated by the dotted line "la is upset to form a band retaining flange lllb at the top of the piston.

Preferably the piston blank employed to carry out the method of my invention is forged or upset according to the disclosures of the co-pending applications of Alfred A. Handler, Serial No. 523,602, filed March 18, 1931, Patent No. 2,024,285, issued December 17, 1935; Serial No. 523,603, filed March 18, 1931, now Patent No. 2,024,286, issued December 17, 1935; and Serial No; 525,277, filed March 25, 1931, now Patent No. 2,096,513, issued October 19, 1937, wherein the metal of the skirt portion of a piston blank is worked by forging to improve the grain structure therein and operative characteristics of the piston. In the event that a piston blank so formed is employed in the practice of the method of the present invention the resultant article will be a piston with a forged skirt and a subsequently forged or upset head portion. In this manner a piston forged throughout may be provided with a piston ring adapter or wear band.

The band II is formed of material sufllciently strong and resilient to resist the expansive forces of the piston body when in service. A steel, bronze or ferrous alloy band may be employed. Prior to the positioning of the band H upon the piston body, preferably the piston and band are each heated to different temperatures dependent upon the piston and band material employed to efiect a shrunk fit of the band upon the piston body. The piston and band while so heated and assembled are placed within a cylindrical die as at l2 and while secured therein the piston is 'subjected to the forging action of the die hammer I3. A core l4 may be arranged within the body of the piston to prevent any deformation in the central part of the head ID or skirt portion IS. The band ll may be provided with spaced internal vertical grooves or notches I 6, providing radially re-entrant portions, prior to assembly with the piston and the metal of the piston body upon being upset will enter said grooves to insure against any rotational movement of the band I with respect to the piston.

The preheating temperatures of the ring and band willbe governed by several selectively variable factors such as, for instance, the material of the piston and the type of piston employed as to whether it is cast or forged. The preheating temperature of the band II will be governed by the shrinking tension desired in the band with respect to the piston and the stress that will be put into-the band by the expansion of the piston body while in service. In any event the temperature difference between the band and the piston at the time of assembly and forging should be such as will maintain a secure shrunk fit of the band within the groove formed by the upsetting, when both the shrinking and upsetting are employed.

Subsequent to the upsetting the piston is cooled and the ring grooves II are machined therein in the usual manner. It will be understood by those skilled'in the art that the band ll may be proportioned to support one ring or several if desired. Where only one piston ring is provided by an adapter or wear resistant bandsuch as H the remaining ring grooves may be machined in the body portion of the piston in the usual manner.

According to the modified form of my invention illustrated in Figure 4 the upper end of the piston body is shaped aslndicated by dotted line. 20a wherein a rounded shoulder portion 20 merges with the vertical and horizontal walls of the annular step or shelf provided at the top of the piston. The ring adapter or wear resistant band 2| of this. embodiment -may be provided with a series of spaced inwardly extending radial projections 22, fonn'ingradially re-entrant portions, arranged to rest on the shoulder 30 of the piston body and in this embodiment the vertical extent of the ring adapter and piston body above the shoulder are proportioned so that the piston head 20 when upset becomes co-planar with the top of the ring adapter.

The ring adapter and piston body of this modification may be subjected to preheating and the ring adapter is preferably shrunk onto the piston in the manner described in connection with the description of the preferred embodiment. Subsequent to heating and assembly of the piston and adapter 2| the parts are placed in a forging apparatus and the portion indicated at 200 is upset to flow into the area above and between the projections 22 to firmly anchor the band to the piston body. The piston may be machined in the usual manner after the forging operation and one or more piston ring. grooves 23 formed in the ring adapter 2|.

It will be understood that the invention is not limited in its broader aspects to the shrunk fit of the band in the groove. The mechanical lock provided by the upsetting of the flange either in the manner shown in Figures 1, 2 and 3 or in the manner shown'in Figure 4 or in other arrangements within the scope of the invention as claimed herein is useful alone particularly where the characteristics of the piston and band are such that the band does not become loosened to such an extent as to cause failure in service. More particularly my invention includes the combination of the mechanical locking provided by the upsetting-and the tight engagement by a shrunk fit under all temperatures encountered in use.

Among the advantages resulting from the above described methods of making a piston is that the method is suited to the working of a forged or upset piston which possesses strength and other desirable characteristics distinguishing it from a cast piston. It will also be observed that the portion of the piston body which overhangs the ring adapter and secures it in position is worked and hardened by the upsetting to form a retaining flange greatly exceeding a cast flange in strength.

While the methods described are particularly m well adapted for the finishing of pistons, especially large pistons, such as employed in Diesel engines, it is also applicable to analogous articles where metals having different characteristics are to be joined to form a composite structure.

Although preferred embodiments of the invention have been described in considerable detail, it is to be understood that modifications and rearrangements may be made without departing from the spirit and scope of the invention as defined in the following claims.

I claim:

1. That method of making a piston which comprises, reducing the diameter of an end portion blank.

2. That method of making a piston which comprises reducing the diameter of an end portion or a light metal piston. blank, arranging a heated wear resistant band on said reduced portion, leaving a part thereof projecting beyond said' band, upsetting the part of said reduced portion projecting beyond said band and flowing the metal therein outwardly into overhanging engagement with said band to secure the band to the piston blank.

3. That method of making a piston which comprises, forming alight metal piston blank with an end portion of reduced diameter, forming a wear resistant band to fit said reduced portion, heating said blank and said band to diiferent temperatures and arranging the band on said redueed blank portion, and pressing the reduced end portion tov flow the metal thereof outwardly to overhang a portion of the band.

4. That method of making a piston which comprises, shaping a light metal piston blank to present an end portion of reduced diameter, cutting and milling a ferrous alloy band to present radially re-entrant portions, heating said blank and band to diiferent temperatures, fitting the band to said reduced portion to efiect a shrunk fit therewith, upsetting the reduced portion to flow the metal thereof outwardly into overhanging and radially interlocking engagement with said band.

5. That method of making a piston which comprises, forging a light metal piston. blank, reducing the diameter of an end portion of the blank, shrinking a wear resistant band on said reduced portion and pressing the reduced end portion to flow the metal thereof outwardly into overhanging'engagement with at least a portion of said band to secure the same to the piston blank.

6. In a light metal piston, a packing ring adapter grooved to receive packing rings secured to a piston-blank with a shrunk fit in a groove having one side thereof formed of upset metal.

7. A light metal piston having a reduced portion adjacent the head end, a wear resistant band arranged to fit said reduced portion and an upset flange constituting the head end of the piston arranged in overhanging engagement with said band.

8. In combination, a forged light metal piston blank having a reduced portion at the head end, a ring adapter grooved to receive packing rings mounted on said reduced portion, an upset flange formed above said ring adapter and engaging same to retain the adapter in position.

9. In combination, a forged piston blank formed of a light metal alloy, said blank having a reduced portion adjacent one end, a wear resistant ring adapter provided with-radlally reentrant portions having shrunk fit engagement with said reduced portion, an upset flange disposed to overhang said ring adapter and have an interlocking fit with said re-entrant portions.

10. In combination, a forged piston blank formed of light metal having a reduced portion at one end to provide an annular shoulder, a wear resistant ring adapter having radial projections extending inwardly supported on said annular shoulder, an upset flange overhanging said projections and filling the spaces between the projections to restrain the ring adapter from axial or rotational movement with respect to the piston blank.

11. That method of making a piston which comprises forming a hollow. light metal cylindrical piston blank with an end portion of reduced diameter, fitting on said reduced end portion a solid circular wear resistant band of heavy metal having a width less than the width of said reduced portion and thereafter upsetting that part of said reduced portion projecting beyond said band to flow the metal outwardly into overhanging engagement with said band to secure said band to the piston blank.

12. A piston comprising a head having a depending cylindrical flange grooved on the outside, and a skirt, a continuous ring seated in said groove and retained in position by an integral upset flange at the head end of the piston.

13. A piston comprising a head having a depending cylindrical flange grooved on the outside, and a skirt, a continuous band seated in said groove and retained in position by an integral upset flange at the head end of the piston, said band being grooved on the outside to receive packing rings.

14. The process of making a piston including forming a piston blank with an end portion of reduced diameter, assembling on said reduced end portion a wear resistant band having a portion projecting radially inward intermediate its upper and lower edges, subjectingthe reduced end portion of the blank to a pressure operation, thereby flowing the metal thereof radially outward into overhanging engagement with the inward projection on said band and substantially flush with the upper edge of said band. I

GEORGE DONALD WELTY. 

